Projection optical system having an angled opitcal part and an offset optical part

ABSTRACT

Provided is a projection optical system which includes a first optical part which projects an image; a second optical part having an image forming device, which forms an image using a light and emits the image to the first optical part; a third optical part having at least one light source which emits the light; and a deflector which guides the light emitted from the third optical part toward the second optical part, wherein an optical axis of the third optical part is angled toward an optical axis of the second optical part, and an optical axis of the first optical part and the optical axis of the second optical part are parallel to each other and separated from each other.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority from Korean Patent Application No.10-2008-0019319, filed on Feb. 29, 2008, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Apparatuses and methods consistent with the present invention relate toan optical system, and more particularly, to a projection optical systemwhich can be used to generate and project an image.

2. Description of the Related Art

In a projection optical system, a light generated by a light source iscondensed, by a condensing lens providing homogeneous illumination, on afilm and then is projected onto a screen via a lens. In order to form animage, a recent projection optical system (disclosed in Japanese PatentNo. 2000-321529, and Japanese Patent No. 2005-092206) does not use thefilm but uses micromirror devices, such as a digital micromirror device(DMD), which are composed of a set of rotary mirrors. Such a projectionoptical system includes an illuminating optics such as the set of rotarymirrors for achieving the homogeneous illumination, and a projectingoptics such as the lens for projecting the image onto the screen.

However, the projection optical system is disadvantageous in that, dueto a relatively long travel distance of light within the projectionoptical system, a considerable loss of light occurs, and this requiresan increase in optical power which may excessively heat the projectionoptical system. In order to prevent such excessive heat, the overallsize of the projection optical system needs to be increased.

According to a projection system disclosed in U.S. Pat. No. 6,439,726,an illuminating optics and a projecting optics of the projection systemare divided into first, second and third optical parts. The first andsecond optical parts have a common optical axis and together compose aprojection lens. The second and third optical parts together compose theilluminating optics. An auxiliary illumination light, such as abacklight, is emitted from the third optical part, is illuminated on thesecond optical part including a micromirror device, forms an imagepattern, is emitted from the projection system and then is projectedonto the screen after having passed through the first optical part. Atthis time, by installing the third optical part at an angle to the firstand second parts, an optical trajectory of the light, that is, adistance between a light source and the micromirror device is shortenedso that loss of light is reduced and the required optical power isreduced. Accordingly, the size of the projection system can be reduced.

However, such a projection system has the following disadvantages. Ingeneral, a compact projection system uses a light source, such as agas-discharge lamp or a light emitting diode, which has greatdivergence. At this time, the light efficiency of a device, the overallsize of the device, and image quality are important features. The higherrequirements to the light efficiency along with application ofhigh-aperture light sources necessitate great numerical aperture of theilluminating light beam falling on the micromirror plate and the greatnumerical aperture of the projection lens. Thus, an aperture diaphragmof the second optical part, wherein the aperture diaphragm is locatedbetween the first optical part and the second optical part, represents apupil plane with respect to both the illumination light and a projectionbeam. A beam splitting in the pupil plane (with the numerical aperturethat is equal to, or that exceeds, sinus of an inclination angle of themicromirror plate) or in its vicinity, minimizes and uniformizes beamvignetting. An acceptable distance depends on the numerical aperture ofthe lens, that is, the smaller the numerical aperture is, the furtherdisplacement of the beam splitting node from the pupil is possible). Ingeneral, such a distance does not exceed a diameter of the pupil. Forefficient separation of an illumination part and a projecting part, anaberration in the pupil is also important. In other words, coincidenceof the position and the size of the pupil for all points of the fieldare important. Also, pupil quality is important not only for theprojecting part, but also for the illuminating part. In the case wherethe illuminating part has great pupil aberrations, the projection systemdemonstrates heterogeneity of vignetting across an image area (field),and increase in an ambient light component, such that optical devicesoverheat and image quality deteriorates. Thus, in order to achieve auniform brightness and generate a high-quality image in the compactprojection system, correction of the pupil of the second optical part isnecessary for both the projection beam and an illumination beam. Bydoing so, an adjustable numerical aperture of the second optical part isincreased. In this case, an applied aperture is asymmetric with respectto the second optical part when the illumination beam reaches the secondoptical part at a great angle. On the other hand, the projection beamgenerally propagates symmetrically or almost symmetrically along anoptical axis.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention overcome the abovedisadvantages and other disadvantages not described above. Also, thepresent invention is not required to overcome the disadvantagesdescribed above, and an exemplary embodiment of the present inventionmay not overcome any of the problems described above. Accordingly, it isan aspect of the present invention to provide a digital TV and a digitalbroadcasting system capable of actively controlling an applicationfunction with efficient use of a limited number of keys when operatingan application program provided by a base broadcasting station byinputting a combination of suitable keys corresponding to the concernedapplication program, thereby controlling the application function, and acontrol method thereof.

The present invention provides a projection system which has a reducedsize and is easy to manufacture by simplifying a structure of a secondoptical part.

According to an aspect of the present invention, there is provided aprojection optical system including a first optical part which projectsan incident image; a second optical part including an image formingdevice which forms an image using a light, and emits the image to thefirst optical part; a third optical part including at least one lightsource, which emits the light; and a deflector which guides the lightemitted from the third optical part toward the second optical part,wherein an optical axis of the third optical part is angled toward anoptical axis of the second optical part, and an optical axis of thefirst optical part and the optical axis of the second optical part areparallel to each other and separated from each other.

An angle formed between the optical axis of the third optical part andthe optical axis of the second optical part may be between 0° and 90°.

A distance between the optical axis of the first optical part and theoptical axis of the second optical part may be between 2% and 50% of anincident pupil diameter of the second optical part.

The deflector may be one of a mirror, a prism, and an apparatusincluding both the mirror and the prism.

The image forming device may be a reflective-type image forming device.

The reflective-type image forming device may be one of a digitalmicromirror device (DMD) and a liquid crystal on silicon (LCOS).

The first optical part includes a first meniscus lens having a firstconcave side, which faces the second optical part; a second meniscuslens having a second concave side, which faces the second optical part;a first positive lens; a third meniscus lens having a third concaveside, which faces the second optical part; a negative lens; and a secondpositive lens.

The second optical part includes a third positive lens; and a cementedlens formed by gluing three lenses.

A first cross-point, which is between the optical axis of the firstoptical part and a pupil plane of the second optical part, may belocated at a position that is distant from a second cross-point, whichis where the optical axis of the second optical part meets the pupilplane of the second optical part, by as much as 0.3 through 3.0 mm.

The third optical part may include a plurality of monochromatic lightsources; a color composition device which combines a light beam from theplurality of monochromatic light sources; and a lens unit which adjustsa numerical aperture and a shape of the light beam combined by the colorcomposition device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will become moreapparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIG. 1 is a diagram of a projection optical system according to anexemplary embodiment of the present invention;

FIGS. 2 and 3 are diagrams of first and second optical parts of theprojection optical system in FIG. 1; and

FIG. 4 is a diagram of a third optical part of the projection opticalsystem in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown. Like reference numerals in the drawings denote likeelements. In the drawings, a size of each component can be exaggeratedfor clarity.

FIG. 1 is a diagram of a projection optical system 100 according to anexemplary embodiment of the present invention. The projection opticalsystem 100 includes a first optical part 1, a second optical part 2, athird optical part 3, and a deflector 4.

The first optical part 1 includes at least one optical device so as toproject an incident image.

The second optical part 2 forms an image by using an incident light, andemits the formed image to the first optical part 1. The second opticalpart 2 includes a reflective-type image forming device 6.

The third optical part 3 includes at least one light source 5, forms andemits a light.

The deflector 4 changes a light path so that the light emitted from thethird optical part 3 is toward the second optical part 2. For example,the deflector 4 may be formed of one of an apparatus including a mirror,an apparatus including a prism, and an apparatus including both a mirrorand prism.

The first optical part 1 and the second optical part 2 together composea projection optics by which the image, which is presented on areflective surface of the reflective-type image forming device 6, isdisplayed on a screen (not shown). The second optical part 2 guides thelight from the light source 5, wherein the light is formed by the thirdoptical part 3 and redirected by the deflector 4.

Here, a pupil plane of the second optical part 2 is located between thefirst optical part 1 and the second optical part 2. The first opticalpart 1, the second optical part 2, and the third optical part 3respectively have optical axes 7, 8, and 9. The optical axis 9 of thethird optical part 3 is angled toward the optical axis 8 of the secondoptical part 2. For example, the optical axis 9 and the optical axis 8form an angle between 0° and 90°.

The optical axis 7 of the first optical part 1 and the optical axis 8 ofthe second optical part 2 are parallel to each other, and are separatedfrom each other. As illustrated in FIG. 1, the optical axis 8 of thesecond optical part 2 is parallel to the optical axis 7 of the firstoptical part 1, and a distance between the optical axis 8 and theoptical axis 7 in a surface passing through the optical axis 7 of thefirst optical part 1 does not exceed a pupil radius of the secondoptical part 2 for a projection beam. For example, the distance betweenthe optical axis 8 and the optical axis 7 may be between 2% and 50% ofan incident pupil diameter of the second optical part 2 for theprojection beam. This value range is selected based on the followingreasons. When de-centering occurs, that is, when the distance betweenthe optical axis 8 of the second optical part 2 and the optical axis 7of the first optical part 1 is smaller than 2% of the incident pupildiameter, a positive effect for reducing the size of the projectionoptical system 100 having an effective vision field becomes negligible.Also, when the distance exceeds 50% of the incident pupil diameter,aberrations may not actually be compensated for.

A first cross-point, which is between the optical axis 7 of the firstoptical part 1 and the pupil plane of the second optical part 2, may belocated at a position that is distant from a second cross-point, whichis where the optical axis 8 of the second optical part 2 meets the pupilplane of the second optical part, by as much as 0.3 through 3.0 mm.

In general, the projection optical system 100 is structured such thatthe third optical part 3 forms a cone shaped light by using the lightfrom the light source 5, and guides the cone shaped light to thedeflector 4. The deflector 4 guides the cone shaped light formed by thethird optical part 3 to the second optical part 2. The light, which haspassed through the second optical part 2 in one direction, is reflectedfrom the reflective-type image forming device 6. Here, thereflective-type image forming device 6 forms the image by using theincident light. Next, the light, which was formed to the image, passesthrough the second optical part 2 in an opposite direction, and reachesan entrance of the first optical part 1. The first optical part 1projects the incident image onto the screen (not shown).

As described above, the first optical part 1 and the second optical part2 are arranged in such a manner that the optical axis 8 of the secondoptical parts 2 is parallel to the optical axis 7 of the first opticalpart 1, and the first optical part 1 and the second optical part 2 areseparated from each other by a distance not exceeding half a pupildiameter of the second optical part 2 with respect to the projectionbeam. By doing so, the projection optical system 100 having a numericalaperture of more than 0.1 is provided.

The projection optical system 100 according to an aspect of the presentinvention partially performs centering for a space in the pupil plane soas to simplify a structure of the second optical part 2 so that anadjustable numerical aperture of the second optical part 2 may bereduced.

FIGS. 2 and 3 are diagrams of the first and second optical parts 1 and 2of the projection optical system 100 in FIG. 1. Referring to FIGS. 2 and3, the first optical part 1 is sequentially arranged toward the secondoptical part 2. The first optical part 1 includes a first meniscus lens10 facing the second optical part 2 with its concave side, a secondmeniscus lens 11 facing the second optical part 2 with its concave side,a first positive lens 12, a third meniscus lens 13 facing the secondoptical part 2 with its concave side, a negative lens 14, and a secondpositive lens 15. The second optical part 2 includes the reflective-typeimage forming device 6, a third positive lens 16, and a cemented lens 17formed by gluing three lenses 17-1, 17-2, and 17-3. The third positivelens 16 and the cemented lens 17 are sequentially arranged from asurface of the reflective-type image forming device 6 toward the firstoptical part 1. For example, a digital micromirror device (DMD), orliquid crystal on silicon (LCOS) that is a reflective-type liquidcrystal display (LCD) may be employed for the reflective-type imageforming device 6.

FIG. 4 is a diagram of the third optical part 3 of the projectionoptical system 100 in FIG. 1. The third optical part 3 includes aplurality of monochromatic light sources 5, a color composition device19 which combines lights from the plurality of monochromatic lightsources 5, and a lens unit 20 which adjusts a numerical aperture and ashape of a light beam combined by the color composition device 19.

Each of the plurality of monochromatic light sources 5 may be a redlight source, a green light source, and a blue light source. The colorcomposition device 19 may be an X-cube used for splitting or combiningof beams. Each of the plurality of monochromatic light sources 5 isdisposed to face each surface of the color composition device 19.

The lens unit 20 adjusts the light beam combined and transmitted by thecolor composition device 19 so as to have a shape and numerical aperturerequested by the projection optical system 100. The lens unit 20 mayinclude a fourth meniscus lens 21 facing the color composition device 19by its concave side, and a fourth positive lens 22.

A light condenser 18 may be arranged between the color compositiondevice 19 and each of the plurality of monochromatic light sources 5.The light condenser 18 is an optical element which reduces angulardivergence of radiation from the plurality of monochromatic lightsources 5, and uniformly condenses the light beam. For example, acompound parabolic concentrator such as a Winston concentrator or afocon may be employed as the light condenser 18. A relatively widersurface of the light condenser 18 is disposed so as to face each of theplurality of monochromatic light sources 5.

An aspect of the present invention has been described herein using acase having three colored (red, green, and blue) light sources, but thepresent invention is not limited thereto.

The aforementioned lenses of the projection optical system according tothe present invention can be manufactured using glass or a plastic. Themanufacturing of the lenses may be possible by using a related artmethod.

The projection optical system according to the present invention can beapplied to all types of projectors, projection television (TV)receivers, displays and other devices using front or rear projection inwhich compactness and a high optical efficiency are required.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the appended claims. Theexemplary embodiments should be considered in a descriptive sense onlyand not for purposes of limitation. Therefore, the scope of the presentinvention is defined not by the detailed description of the presentinvention but by the appended claims, and all differences within thescope will be construed as being included in the present invention.

1. A projection optical system comprising: a first optical part whichprojects an incident image; a second optical part including an imageforming device which forms an image using a light and emits the image tothe first optical part; a third optical part including at least onelight source which emits the light; and a deflector which guides thelight emitted from the third optical part toward the second opticalpart, wherein an optical axis of the third optical part is angled towardan optical axis of the second optical part, and an optical axis of thefirst optical part and the optical axis of the second optical part areparallel to each other and separated from each other, wherein theoptical axes of the first, second and third optical parts extend alongrespective paths of the light from the first, second and third opticalparts, wherein a distance between the optical axis of the first opticalpart and the optical axis of the second optical part is between 2% and50% of an incident pupil diameter of the second optical part, andwherein the optical axis of the third optical part extends through thefirst optical part.
 2. The projection optical system of claim 1, whereinan angle formed between the optical axis of the third optical part andthe optical axis of the second optical part is between 0° and 90°. 3.The projection optical system of claim 1, wherein the deflector is oneof a mirror, a prism, and an apparatus including both the mirror and theprism.
 4. The projection optical system of claim 1, wherein the imageforming device is a reflective-type image forming device.
 5. Theprojection optical system of claim 4, wherein the reflective-type imageforming device is one of a digital micromirror device (DMD) and a liquidcrystal on silicon (LCOS).
 6. The projection optical system of claim 1,wherein the first optical part includes: a first meniscus lens having afirst concave side which faces the second optical part; a secondmeniscus lens having a second concave side which faces the secondoptical part; a first positive lens; a third meniscus lens having athird concave side which faces the second optical part; a negative lens;and a second positive lens, wherein the first meniscus lens, the secondmeniscus lens, the first positive lens, the third meniscus lens, thenegative lens and the second positive lens are sequentially arranged ina direction toward the second optical part.
 7. The projection opticalsystem of claim 1, the second optical part includes: a positive lens;and a cemented lens formed by gluing three lenses, wherein the positivelens and the cemented lens are sequentially arranged in a directiontoward the first optical part.
 8. The projection optical system of claim1, wherein a pupil plane of the second optical part is located betweenthe first optical part and the second optical part, and wherein a firstcross-point, which is between the optical axis of the first optical partand the pupil plane of the second optical part, is located at a positionthat is distant from a second cross-point, which is where the opticalaxis of the second optical part meets the pupil plane of the secondoptical part, by as much as 0.3 through 3.0 mm.
 9. The projectionoptical system of claim 1, wherein the third optical part includes: aplurality of monochromatic light sources; a color composition devicewhich combines a light beam from the plurality of monochromatic lightsources; and a lens unit which adjusts a numerical aperture and a shapeof the light beam combined by the color composition device.
 10. Theprojection optical system of claim 9, wherein the color compositiondevice is an X-cube, each of the plurality of monochromatic lightsources faces each surface of the X-cube, and a light condenser isarranged between the X-cube and each of the plurality of monochromaticlight sources.
 11. The projection optical system of claim 9, wherein thelens unit includes a meniscus lens having a concave side facing thecolor composition device, and a positive lens.